1. Field of the Invention
This invention relates, in general, to optical field effect transistors (OPFET) and, more particularly, to edge illuminated OPFET photodetectors.
2. Description of the Background
Typical OPFET photodetectors have an optic fiber butt coupled to the planar surface thereof to provide a light source. Butt coupling suffers from the fact that a significant fraction of the light is actually absorbed in the semi-insulating substrate, which is inherently slow in its photo-conductive properties. This light will then either dissipate, recombine, or produce electron-hole pairs which diffuse back into the channel. This diffusion into the channel causes the signal to be extended effectively reducing the frequency of the signals that may be transmitted. As a result, OPFET devices are characterized by both a low frequency and a high frequency response. This is not unusual, since even silicon PIN diodes have a difference between low and high frequency behavior. However, because of the inherently thin layers used in the GaAs MESFET devices, there is a very large difference between low and high frequency performance. In addition, the GaAs OPFET devices are by no means optimized for optical coupling from a single mode fiber.